When evaluating cotton twill, the yarn count (e.g., 20s, 30s, 40s) and thread count (density) are the primary indicators of quality. A higher yarn count typically results in a finer, softer fabric, while a lower count indicates a heavier, more durable material suitable for workwear. You must also verify the weight (GSM - Grams per Square Meter); for instance, 190-240 GSM is standard for trousers, while lighter weights are used for shirts. Additionally, confirm the weaving pattern (e.g., 2/1 or 3/1 twill), as this determines the prominence of the diagonal ribbing and the fabric's overall drape and tear resistance.